ffmpeg -y -loglevel warning -i video5.mp4 -i video7.mp4 -filter_complex \
"nullsrc = size = 640*640 [base]; \
[0:v] setpts=PTS-STARTPTS, scale=320x640 [left]; \
[1:v] setpts=PTS-STARTPTS, scale=320x640 [right]; \
[base][left] overlay=shortest=1:x=0:y=0 [tmp1]; \
[tmp1][right] overlay=shortest=1:x=320[vout]; \
[0:a][1:a]amerge=[a]" \
-map "[vout]" -map "[a]" -ac 2 output5and7high.mp4

OUTPUT:-
[Parsed_amerge_7 @ 0x7fbe5ae0a280] No channel layout for input 1
unknown side data type 10 (24 bytes)